Microgrids are providing a growing percentage of the electric power consumed by electronic devices located on and away from microgrid locations. As more microgrids are connected with the bulk electric system (BES), the complications of microgrid control for both operators of the BES and of microgrids become more evident.
Although the concept of a microgrid has been known within the electrical utility industry for many years as a small scale electricity system, recent advances in material sciences and information technology, among others, have facilitated improved techniques and methodologies making microgrid installations more reliable, practical, and attractive for an increasing segment of electrical loads. The benefits of microgid installations are also well known in the industry. Generation sources within a typical microgrid are frequently from renewable resources and suffer less distribution system loss traveling much shorter distance from source to load. Microgrids also allow more user control over electricity consumption and creation, allowing increased security and reliability for some microgrid users as well as independence from traditional utilizes.
As interest and availability of microgrids increase, so too does their impact on the BES. While the typical microgrid covers a smaller area with a small number of power generation sources and loads, such as a single office building load serviced by generation from a small number of wind turbines, photovoltaics and traditional generation sources, the size varies greatly and can include any number of generation and load assets. Many such microgrids are connected to and, to some degree, dependent upon connection with the bulk electrical system for reliability, creating a “back-and-forth,” transactional relationship with local utilities and energy markets.
Many microgrids utilize some form of a master controller to facilitate data acquisition and perform monitoring and supervisory control over the operation of a microgrid during all microgrid operating modes (grid-connected, islanded, and transition between the two). In the current state of the art, master controllers have monitored the prevailing operating conditions of a microgrid and initiated pre-programmed, remedial actions if the system is not operating within acceptable limits (e.g. voltage and frequency violations). Microgrid master controllers have been designed with functionality to dispatch local resources to minimize the overall cost of meeting microgrid load by balancing generation and load reactively or in near-real time in order to reduce the purchase of electricity supply from the BES.
The size and complexity of microgrid installations utilizing many generation sources to fulfill demand within the microgrid, in whole or part, creates challenges for both the microgrid operator as well as any utilities that would like to anticipate demand from one or multiple microgrid installations as well as economically utilize any excess generation.
Historically, the ability to forecast demand within a microgrid and effectively balance generation to meet predicted, local load demands has been inaccurate and unreliable. Some microgrids have relied primarily on producing additional generation to ensure reliability. Without methods for accurately forecasting demand within a local system, excess generation created by such a microgrid must be stored or reintroduced to the BES. This too has caused additional issues for utilities that must identify load entering the BES and find methods to economically utilize that additional generation in a manner which does not violate strict reliability regulations. Moreover, such generation can be expensive to both purchase and utilize for utilities, while syncing excess generation for distribution to the BES can be difficult and unreliable for microgrid system operators as well.
Further, the ability to optimize microgrid activities has been hindered by the lack of a reliable valuation of dispatchable load. Without this valuation, microgrid managers do not have a clear conception of the true cost of the “generation” (by means of load shedding) employed to provide the microgrid's demanded load. Thus, unseen costs associated with shedding dispatchable load counteract the economic benefits of shedding that load in lieu of increasing generation or purchasing electricity from the BES. This decreases the usefulness of microgrid optimization activities, as these unseen costs may outweigh the apparent financial benefit of load shedding in certain situations.